The use of LCST polymers as controlled release systems is, e.g., known from U.S. Pat. No. 5,720,976. In this publication release systems are disclosed, wherein an active ingredient is encapsulated in liposomes. LCST polymers are grafted to the surface of liposomes. By choosing the ratio of respective monomers in the LCST polymers, the LCST value of the polymers can be adjusted.
Furthermore, WO-A-92/07881 discloses that the solubility of polyacrylamide changes as a result of the presence of amide groups, which groups have a buffering effect. This pertains to the solubility per se, not to the LCST, which is not mentioned in this publication.
Also in EP-A-0 693 508 and in DE-A-4 023 578, it is described that the temperature sensitivity of certain polymers can be influenced by varying the ratio of the comonomers present in these certain polymers.
None of these prior art documents teach or suggest however, that LCST polymer systems can be modified, as is done in accordance with the present invention in such a way, that the LCST value of the polymers changes during incubation and as a result of incubation, and by which the above mentioned advantages of the present invention can be obtained.